Modern aircraft are equipped with an environmental control system (ECS) that provides air supply, thermal control, and cabin pressurization for the aircraft. An ECS typically includes various components, such as a bleed system, air conditioning pack, mix manifold, recirculation system, and cabin ventilation system.
In operation, an aircraft's bleed system extracts compressed air from one of multiple bleed ports on one of the aircraft's engines and provides air to other components of the ECS. For instance, the bleed system may supply air to one of the aircraft's air conditioning packs.
An air conditioning pack is an air cycle refrigeration system that uses outside air at ambient temperature and pressure as the coolant. The air conditioning pack outputs cold, conditioned air. In some instances, the cold air may even be below freezing (i.e., at a temperature of less than 32° F.). The cold air leaving the air conditioning pack then travels via a pack source duct to a mixing chamber, referred to as a “mix manifold”, where the cold air is mixed with filtered recirculated air from the aircraft's cabin.
The mix manifold, in turn, supplies air to the aircraft's cabin ventilation system. The cabin ventilation system supplies air to various seating zones of the aircraft's cabin. Within the cabin ventilation system, the air is mixed with trim air (i.e. hot bleed air from the aircraft's bleed system or an electric motor driven compressor) to raise the temperature of the air to an appropriate temperature for various seating zones of the cabin.
Some aircraft include a separate duct that provides air to the aircraft's flight deck. This separate duct is commonly referred to as a flight deck duct. In one example, the flight deck duct may branch off of the pack source duct at an angle, such that a portion of the conditioned air traveling from the air conditioning pack to the mix manifold is diverted to the flight deck without entering the mix manifold. Trim air may also be injected into the flight deck duct to raise the temperature of the air supplied to the flight deck.